Exercise is an integral part of life for millions of Americans. The benefits of exercise are well- known-improvement in longevity and quality of life (QOL). However, while data on safety of exercise for patients with genetic cardiovascular conditions, such as the long QT syndrome (LQTS), and hypertrophic cardiomyopathy (HCM,) are sparse, the risk of sudden cardiac death due to vigorous competitive or recreational activities for these patients is thought to be prohibitively high and these patients are restricted from participation in not just competitive, but most recreational sports as well, by current consensus statements in both the US and Europe. However, preliminary data suggest that first, many patients with these conditions are exercising despite the restrictions and second, that the risks may be lower than postulated, and that there may be detrimental effects of exercise restriction in these patients. Whether the risks of exercise outweigh the medical and quality-of-life benefits for patients with these LQTS and HCM has never been evaluated prospectively. This study will prospectively investigate the risks and benefits of exercise for patients with LQTS and HCM in parallel observational cohorts. The study will evaluate the hypothesis that risks of death, cardiac arrest, syncope, or appropriate ICD therapy will not be higher in those exercising moderately or vigorously than the sedentary, and that quality of life will be greater in those exercising. Individuals with HCM and LQT who have chosen to continue to exercise will be identified and enrolled both through traditional recruiting sites, and through partnering with patient-advocacy organizations and less active patients will be enrolled as a comparator group. These subjects will then be followed prospectively for three years. Results of this study will have an immediate and direct impact on patient care. If the hypotheses are correct, many more individuals will enjoy the benefits of exercise. If the hypotheses prove incorrect, those currently exercising need to know, and exploratory aims will investigate what phenotypic, clinical, genotypic, and sports-related factors may moderate the impact of exercise on arrhythmic outcomes, and will identify clinical and psychological variables which may moderate the impact of exercise restriction on quality of life.